This competing renewal application investigates the persistence, ecology and surveillance of mosquito-borne encephalitis viruses in seasonal wetland and agricultural habitats in California. Proposed research tests the hypothesis that resident and/or transient birds associated with seasonal wetlands are responsible for the interseasonal maintenance and vernal amplification of western equine encephalomyelitis (WEE) and St. Louis encephalitis (SLE) viruses and serves as a source of virus for adjacent and distant receptive habitats. Virus ecology at wetlands in the Coachella Valley of southeastern California with consistent enzootic activity will be compared with wetlands in the southern San Joaquin Valley where virus activity currently is intermittent.